Sensory disturbances are frequently encountered in patients with peripheral neuropathy and these deficiencies are well known to produce serious disabilities. Electrodiagnosis, an essential tool for detection of abnormal nerve function, is typically achieved by recording the compound action potential in response to electrical nerve stimulation. Although this approach has provided some information of basic nerve conduction in health and disease its interpretation and diagnostic range are limited. Mass recording from peripheral nerve does not provide details of the functional state of the many different types of axons of which it is composed. Achieving such detail requires unitary analysis of identified primary afferent axons in response to natural stimulation of their sensory receptors. This can be accomplished with the technique of percutaneous microneurography, in which tungsten microelectrodes are inserted into peripheral nerves and the action potentials of single afferent axons are recorded and carefully characterized. The present investigation proposes to study the properties of primary afferent axons in sensory neuropathies, using the technique of percutaneous microneurography, and to correlate these findings with the outcome of routine clinical procedures. The encoding properties and receptive field organization of identified peripheral afferents will be investigated in response to physiologic stimulation of the receptor organs. In addition conduction velocity measurements will be made and individual sensory axons will be activated by electrical microstimulation so that the quality, intensity and projection of perceived sensations from different types of afferents during different stages of nerve degeneration can be assessed. Unitary analysis permits direct study of the generation and transmission of nerve impulses, making it possible to study details of the pathophysiology of peripheral nerves which are inaccessible to conventional electrodiagnosis. This direct approach of studying the response behavior of diseased afferent nerve fibers will contribute substantially to the neurological diagnostic repertoire. Direct assessment of the functional state of identified afferents provides a more sensitive assay for an objective evaluation of the course and efficacy of therapeutic procedures than has heretofore been available.